How is the thermal resistance PT100 connected to two measuring instruments?
Four line: at both ends of the root of thermal resistance is connected to each of the two wires is called the four line, the two leads for thermal resistance to provide a constant current I, convert R to U voltage, and then through the other two leads to U to two meters. It can be seen that this lead way can completely eliminate the influence of lead resistance, mainly used for high-precision temperature detection.
Three wire connection lead wire at one end of the thermal resistance of the root, the other end is connected to two leads the way is called the three wire, usually with the bridge supporting the use, can eliminate the influence of wire resistance is good, the lead resistance most commonly used in industrial process control.
Two-wire: at both ends of the thermal resistance is respectively connected with a wire leads to the resistance of the two-wire mode called: this wire method is very simple, but because the connecting wires must exist lead resistance factors of R and R, the size and the length of the wire material, so this leads only suitable for situations with low measurement accuracy
The thermal resistance is connected by three wire system. The three wire system is used to eliminate the measurement errors caused by the resistance of the connecting wires. This is because the circuit measuring thermal resistance is generally unbalanced bridge. Thermal resistance as a bridge arm resistance bridge, the connecting wires (from thermal resistance to the control room) has become a part of the bridge arm resistance, this part of resistance is unknown and the change of ambient temperature, caused by measurement error. The three wire system is used to connect one wire to the power supply of the bridge, and the other two are connected to the bridge arm of the thermal resistance and the bridge arm adjacent to it, thus eliminating the measurement error caused by the resistance of the wire line. Generally, three wire connection is adopted in industry. The thermocouple produced is MV, and there is no such problem.
